1. Technical Field
The present invention relates to a polarization control device, a polarization control method, and an image display system for performing three-dimensional image display.
2. Related Art
In the past, there has been proposed an image display device for expressing the display image in a three-dimensional manner (see, e.g., JP-A-02-144516 (Document 1)). In this technology, the observer selectively views two parallax images (a right-eye image and a left-eye image described later), which are shifted an amount corresponding to the observing points of the right eye and the left eye with the respective eyes to thereby visually recognize the display image in a three-dimensional manner. Further, there has also been proposed a technology with which a plurality of observers can visually recognize respective images different from each other when the plurality of observers views the projection image from the respective directions different from each other.
As the method of stereoscopically displaying an image, there are known a wavelength separation system, a time-division system, a polarized light system, and so on. The wavelength separation system is a system for projecting two parallax images having respective wavelengths different from each other, and then separating the two parallax images by the difference in wavelength and sorting them into the left eye and the right eye. The time-division system and the polarized light system are advantageous over the wavelength separation system in color reproducibility.
The polarized light system is a system of polarizing the polarization direction of the light emitted from the liquid crystal projector or the liquid crystal display device into two parallax images having respective polarization directions different from each other using a polarization control device in an image display system, and then separating the two parallax images by the difference in polarization direction using a pair of polarization spectacles to thereby sort the two parallax images into the left eye and the right eye (see, e.g., Document 1). In the polarized light system, a silver screen or the like on which the light is difficult to be scattered is used so that the polarization direction is kept before and after the light from, for example, the projector is reflected by the projection surface.
However, in the configuration of Document 1, since the stereoscopic display is performed by the polarized light system using a single projector, the configuration shown in FIG. 8 is adopted as the image display device. The light L1 emitted from the projector PJ is transmitted through the polarization plate 11, then the light L3 is projected on the screen SR after being transmitted through the liquid crystal panel 12, and thus the image is displayed in an enlarged manner.
Here, in the polarized light system shown in FIG. 8, the polarized lights different from each other are projected on the screen in a time-divisional manner in order to perform the stereoscopic display of the image.
Therefore, as shown in FIG. 9, the control voltage is applied to the liquid crystal panel 12 having the slow axis at an angle of 45° with the transmission axis of the polarization plate 11 in a time-divisional manner in sync with the timing at which the projector PJ sequentially emits the light L1 of the right-eye image and the left-eye image. For example, since the right-eye image is emitted from the projector PJ in the period from the time point t1 to the time point t2, the control section 10 provides the liquid crystal panel 12 with the control signal of setting the phase difference to λ/4. On the other hand, since the left-eye image is emitted from the projector PJ in the period from the time point t2 to the time point t3, the control section 10 provides the liquid crystal panel 12 with the control signal of setting the phase difference to −λ/4. The process of changing the phase difference is performed in a time-divisional manner.
Thus, the liquid crystal panel 12 emits the light L3 as the right circularly polarized light (e.g., the right-eye image) when the light L2 with the vertical polarization is controlled to have the phase difference of λ/4, or emits the light L3 as the left circularly polarized light (e.g., the left-eye image) when it is controlled to have the phase difference of −λ/4. On this occasion, the control section 10 generates the signal for controlling the phase difference based on the information for distinguishing the right-eye image data and the left-eye image data from each other included in the image data supplied to the projector PJ, and then outputs the signal to the liquid crystal panel 12.
Here, the polarization plate 11 is for aligning the polarization of the light L1 input from the projector PJ. In general, although the light L1 is emitted from the projector PJ as the vertically polarized light, the horizontally polarized light is included as a partial component. Therefore, in order to prevent the crosstalk between the right-eye image and the left-eye image, the polarization plate 11 emits only the vertically polarized light component in the light L1 to the liquid crystal panel 12 in the next stage.
A pair of spectacles 50 is worn by the observer in order to view the image displayed on the screen SR as a stereoscopic image. Since the light L3 emitted from the liquid crystal panel 12 is reflected by the screen to thereby be changed to the left circularly polarized light from the right circularly polarized light, or to the right circularly polarized light from the left circularly polarized light, the pair of spectacles 50 for observation (hereinafter also referred to as a pair of observation spectacles 50) is provided with an optical element having a property of transmitting the right circularly polarized light (the left-eye image) disposed on the surface of the left glass 50L, and an optical element having a property of transmitting the left circularly polarized light (the right-eye image) disposed on the surface of the right glass 50R.
Therefore, by wearing the pair of observation spectacles 50, the observer can observe the stereoscopic image in a “pseudo” manner due to the human visual feature since the left eye views the left-eye image and the right eye views the right-eye image.
Further, in response to the supply of the right-eye image data (or the left-eye image data) from an external device (not shown), the projector PJ processes the light L1 for the left-eye image (or the right-eye image) and then outputs the light L1 in a time-divisional manner.
Here, since the converged intense light enters the liquid crystal panel used in the projector PJ, the liquid crystal panel using a liquid crystal material with a high durability is used to avoid the problem of lifetime. However, the liquid crystal material with a high durability takes a long time for varying the orientation of the liquid crystal from when the signal has been applied, and the orientation of the liquid crystal varies gradually. Therefore, as shown in FIG. 9, it results that the orientation of the liquid crystal varies with a time constant until it completely varies from the outgoing light L1 of the left-eye image to the outgoing light L1 of the right-eye image.
On the other hand, since the light L1, which is diffused light, from the projector PJ enters the liquid crystal panel 12 of the polarization control device 100, the liquid crystal panel 12 is not required to have very high durability, and therefore, the liquid crystal with a high rate of variation in the orientation of the liquid crystal is used for the liquid crystal panel 12.
Therefore, the control section 10 applies the signal for controlling the phase difference to the liquid crystal panel 12 at a timing shifted by the time ΔT from the timing at which the image data is switched from either one of the right-eye image data and the left-eye image data to the other.
However, since the timing at which the image data is switched from either one of the right-eye image data and the left-eye image data to the other is different between the orientation states of the liquid crystal, it is unachievable to make the time ΔT constant, and therefore, it is unachievable to completely suppress the crosstalk at the switching timing.
FIG. 9 is a waveform chart showing the control performed when the right-eye image represents all white and the left-eye image represents all black for the sake of explanation. The light of the right-eye image due to the crosstalk enters the left-eye though the left-eye image represents the black display, and it causes blur of the image in the stereoscopic view, and results in the degradation in quality of the display image.